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<!DOCTYPE html>
<html>

<head>
  <script data-require="d3@3.5.3" data-semver="3.5.3" src="//cdnjs.cloudflare.com/ajax/libs/d3/3.5.3/d3.js"></script>
  <style>
    body {
      font: 10px sans-serif;
    }
    
    .axis path,
    .axis line {
      fill: none;
      stroke: #000;
      shape-rendering: crispEdges;
    }
    
    .x.axis path {
      display: none;
    }
    
    .line {
      fill: none;
      stroke: steelblue;
      stroke-width: 1.5px;
    }
  </style>
</head>

var margin = {
        top: 20,
        right: 80,
        bottom: 30,
        left: 50
      },
      width = 500 - margin.left - margin.right,
      height = 500 - margin.top - margin.bottom;

var parseDate = d3.time.format("%Y%m%d").parse;

var x = d3.time.scale()
      .range([0, width]);

var y = d3.scale.linear()
      .range([height, 0]);

var color = d3.scale.category10();

var xAxis = d3.svg.axis()
      .scale(x)
      .orient("bottom");

var yAxis = d3.svg.axis()
      .scale(y)
      .orient("left");

var line = d3.svg.line()
      .interpolate("basis")
      .x(function(d) {
        return x(d.date);
      })
      .y(function(d) {
        return y(d.temperature);
      });

var svg = d3.select("body").append("svg")
      .attr("width", width + margin.left + margin.right)
      .attr("height", height + margin.top + margin.bottom)
      .append("g")
      .attr("transform", "translate(" + margin.left + "," + margin.top + ")");

d3.tsv("data.tsv", function(error, data) {
 
  color.domain(d3.keys(data[0]).filter(function(key) { return key !== "date"; }));
 
    data.forEach(function(d) {
      d.date = parseDate(d.date);
    });

x.domain(d3.extent(data, function(d) {
      return d.date;
    }));

y.domain([
      d3.min(cities, function(c) {
        return d3.min(c.values, function(v) {
          return v.temperature;
        });
      }),
      d3.max(cities, function(c) {
        return d3.max(c.values, function(v) {
          return v.temperature;
        });
      })
    ]);

var legend = svg.selectAll('g')
      .data(cities)
      .enter()
      .append('g')
      .attr('class', 'legend');

legend.append('rect')
      .attr('x', width - 20)
      .attr('y', function(d, i) {
        return i * 20;
      })
      .attr('width', 10)
      .attr('height', 10)
      .style('fill', function(d) {
        return color(d.name);
      });

legend.append('text')
      .attr('x', width - 8)
      .attr('y', function(d, i) {
        return (i * 20) + 9;
      })
      .text(function(d) {
        return d.name;
      });

svg.append("g")
      .attr("class", "x axis")
      .attr("transform", "translate(0," + height + ")")
      .call(xAxis);

svg.append("g")
      .attr("class", "y axis")
      .call(yAxis)
      .append("text")
      .attr("transform", "rotate(-90)")
      .attr("y", 6)
      .attr("dy", ".71em")
      .style("text-anchor", "end")
      .text("Test Graph (1)");

var city = svg.selectAll(".city")
      .data(cities)
      .enter().append("g")
      .attr("class", "city");

city.append("path")
      .attr("class", "line")
      .attr("d", function(d) {
        return line(d.values);
      })
      .style("stroke", function(d) {
        return color(d.name);
      });

city.append("text")
      .datum(function(d) {
        return {
          name: d.name,
          value: d.values[d.values.length - 1]
        };
      })
      .attr("transform", function(d) {
        return "translate(" + x(d.value.date) + "," + y(d.value.temperature) + ")";
      })
      .attr("x", 3)
      .attr("dy", ".35em")
      .text(function(d) {
        return d.name;
      });

var mouseG = svg.append("g")
      .attr("class", "mouse-over-effects");

mouseG.append("path") // this is the black vertical line to follow mouse
      .attr("class", "mouse-line")
      .style("stroke", "black")
      .style("stroke-width", "1px")
      .style("opacity", "0");
      
    var lines = document.getElementsByClassName('line');

var mousePerLine = mouseG.selectAll('.mouse-per-line')
      .data(cities)
      .enter()
      .append("g")
      .attr("class", "mouse-per-line");

mousePerLine.append("circle")
      .attr("r", 7)
      .style("stroke", function(d) {
        return color(d.name);
      })
      .style("fill", "none")
      .style("stroke-width", "1px")
      .style("opacity", "0");

mousePerLine.append("text")
      .attr("transform", "translate(10,3)");

mouseG.append('svg:rect') // append a rect to catch mouse movements on canvas
      .attr('width', width) // can't catch mouse events on a g element
      .attr('height', height)
      .attr('fill', 'none')
      .attr('pointer-events', 'all')
      .on('mouseout', function() { // on mouse out hide line, circles and text
        d3.select(".mouse-line")
          .style("opacity", "0");
        d3.selectAll(".mouse-per-line circle")
          .style("opacity", "0");
        d3.selectAll(".mouse-per-line text")
          .style("opacity", "0");
      })
      .on('mouseover', function() { // on mouse in show line, circles and text
        d3.select(".mouse-line")
          .style("opacity", "1");
        d3.selectAll(".mouse-per-line circle")
          .style("opacity", "1");
        d3.selectAll(".mouse-per-line text")
          .style("opacity", "1");
      })
      .on('mousemove', function() { // mouse moving over canvas
        var mouse = d3.mouse(this);
        d3.select(".mouse-line")
          .attr("d", function() {
            var d = "M" + mouse[0] + "," + height;
            d += " " + mouse[0] + "," + 0;
            return d;
          });

d3.selectAll(".mouse-per-line")
          .attr("transform", function(d, i) {
            console.log(width/mouse[0])
            var xDate = x.invert(mouse[0]),
                bisect = d3.bisector(function(d) { return d.date; }).right;
                idx = bisect(d.values, xDate);
            
            var beginning = 0,
                end = lines[i].getTotalLength(),
                target = null;

while (true){
              target = Math.floor((beginning + end) / 2);
              pos = lines[i].getPointAtLength(target);
              if ((target === end || target === beginning) && pos.x !== mouse[0]) {
                  break;
              }
              if (pos.x > mouse[0])      end = target;
              else if (pos.x < mouse[0]) beginning = target;
              else break; //position found
            }
            
            d3.select(this).select('text')
              .text(y.invert(pos.y).toFixed(2));
              
            return "translate(" + mouse[0] + "," + pos.y +")";
          });
      
      
  </script>
</body>

</html>

https://cdnjs.cloudflare.com/ajax/libs/d3/3.5.3/d3.js